Gerardo Martino suffered his first loss as Barcelona's head coach on Tuesday, as they went down 2-1 at Ajax in the UEFA Champions League.
The defeat came despite Ajax being reduced to 10 men for over 40 minutes as, with the exception of Xavi’s second-half penalty, Barca were unable to find a way through the resilient defence of their hosts.
And midfielder Cesc Fabregas admitted the reigning Spanish champions need to play with more intensity if they are to continue their stunning start to the league campaign, which has seen them take 40 points from a possible 42.
"We've had a team chat with the coach," Fabregas said.
"There's always self-criticism, but this was the season's first defeat and we have to react.
"We have to move the ball faster, show more motivation, attack with the ball and be intense, both in defence and attack."
Barcelona have not lost in their 14 La Liga matches this season, winning 13 and drawing once.
They are only three points ahead of Atletico Madrid, but lead fierce rivals Real Madrid by six, despite an injury crisis that has seen many of their stars sidelined.
None are more notable than Lionel Messi (thigh), with the Argentina forward - who has scored 50 and 46 goals in his last two La Liga seasons - not having played since November 10.
Messi is not expected back until the new year, while first-choice goalkeeper Victor Valdes (calf) is also sidelined.
Dani Alves has missed the club's last two matches with a calf issue of his own, while left-back Jordi Alba (hamstring) and midfielders Jonathan dos Santos and Isaac Cuenca (both knee) are long-term absentees.
Barca will welcome the in-form back Alexis Sanchez back from suspension, though. Alexis has scored eight goals in his last eight matches for club and country and Martino will be delighted by his return, especially given the continued absence of talisman Messi.
The corresponding fixture last season ended in a 2-2 draw in April, but Barcelona romped to a 5-1 success at Camp Nou.
Athletic have not beaten Barcelona since May 2006, when they posted a 3-1 home win, and they would love a repeat as they battle it out with Villarreal for fourth position on the table.
Ernesto Valverde's side sit fifth, six points clear of their nearest rival, and reaching the Champions League is their aim.
A lack of goals has stunted their progress, though, with not one player in the squad having netted more than three league goals.
However, Athletic have not lost in their last seven La Liga home games and are sure to provide Barca with a stern test.
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